With most Pokémon, it isn't a matter of if their Shiny forms will be released in Pokémon GO… it's a matter of when. Generally, with Legendary Raid Bosses, Niantic will release them in their non-Shiny form for their in-game debut, remove them from the raid rotation for a while (or, in the case of Palkia and Dilga, for what feels like centuries), and then re-release them with Shiny potential. With Pokémon that can be caught in the wild, Niantic will usually tie their Shiny release to an event. There is one type of Pokémon that trainers have been speculating over for years, though: the Special Research only Mythical Pokémon such as Mew, Celebi, Jirachi, and Victini. There are meant to be only one of these Pokémon per account… so when and how can Niantic ever release Shiny Mew?
Shiny Mew is one of the best Shiny Pokémon in the game, with a light blue color that complements its eyes. The design is stellar, and one that any trainer will want to be added to their collection. It remains uncertain if it will ever be released, but it is in the game's code.
There would have to be a major change to the mechanics of Mew before its Shiny form is released. The "every player gets one" wouldn't work when trainers are attempting to hunt a Shiny, so a second Special Research ending in one encounter won't work. What would be the best option would likely be EX Raids. These invite-only raids, pre-Remote Raid Invites, were earned by players by competing in EX-eligible gyms. Previous bosses included Mewtwo as well as the mythical Pokémon Deoxys, which sets a precedent for a Mythical Pokémon to have an EX run.
Shiny Mew being released through EX Raids would also be a terrific way to bring this form of raiding back, as these were canceled during the lockdown. Genesect was meant to be the next EX Raid boss but has since been introduced into regular raids with its Shiny already available. Remote Raid Invites may have made EX Raids seem obsolete, which Niantic would be able to fix with a Shiny Mew EX release. Not only would it invigorate the system, but it would also give Pokémon GO trainers a shot at getting a Pokémon that is rare beyond rare in the main series games.